1. Field of the Invention
This invention relates to ceramics, and more particularly to improving the properties of ceramic zirconia.
2. Description of the Previously Published Art Because of its toughness, wear resistance, harness, low thermal conductivity, and other properties, zirconia (ZrO.sub.2) has found numerous ceramic applications. Typical of these uses (e.g., in gasoline or diesel engines) are wear buttons for valve tappets; valve seats; oxygen sensor sleeves; piston caps (for diesels), and precombustion chamber elements (for diesels). Typical non-auto engine uses include grinding balls, dies, check valves and the like.
As described in my related patent, U.S. Pat. No. 4,891,343, of Jan. 2, 1990, tetragonal zirconia, the most commonly used form of zirconia, can exist at room temperature, but is meltable and under stress tends to transform to the monoclinic form, with increase in volume and loss of various important properties.
Various modifications and/or treatments of zirconia have been tried in efforts to minimize conversion of tetragonal to the monoclinic form. One approach is to add a stabilizer containing expensive dysprosia (Dy.sub.2 O.sub.3) to the tetragonal zirconia.